The application of germicides, heat and the like has been commonly practiced in order to kill various kinds of cells such as bacteria, microscopic algae, blood corpuscles, and animal and plant cells.
In the treatment of foodstuffs, pharmaceuticals, and various animals and plants, however, these processes have often produced undesirable effects such as denaturation of the material and side effects. In particular, the development of simple and significantly effective cytocidal processes is much sought after in such areas as the sterilization of drinking water, killing algae inhibiting the growth of farm crops, and killing tumorous cells. In Japanese patent application No. 58-221388, the present inventor proposed a process for the selective control of cellular activity by the application of a prescribed voltage to cells. This process involves applying scanning electric potentials on cells, using techniques such as cyclic voltammetry, differential polarography, and phase discrimination AC polarography to obtain measured values of the electric currents generated. The process enables cellular activities such as respiratory activity to be selectively and effectively inhibited and controlled by externally applying to the cells an electric potential that is close to the value of a potential giving the ultimate value characteristic to cells of the current-potential curve or the ultimate value of a differential electric current (peak potential value), and furthermore, it enables bactericidal or antimicrobial control to be achieved. Taking advantage of this principle, a process that comprises allowing photosemiconductors such as TiO.sub.2 and the like to carry conductors such as Pt and the like, and utilizing the photoelectromotive force generated by these particles to directly apply said peak potential to various cells to kill them has been proposed. Each of these cytocidal processes uses a photosemiconductor carrying a conductor. Such cytocidal processes using conductor-carrying photosemiconductors are, however, not completely satisfactory. For example, where metals other than platinum are used as conductors, since they are liable to elute into the material subjected to sterilization while in use, these metals cannot be used for such purposes as the sterilization of drinking water. On the other hand, where platinum is used as a conductor, the cost of cell-killing is exorbitant because it is an expensive metal. For these reasons, a cytocidal process which does not impart metals to the material under cytocidal treatment and can be implemented at a low cost is much sought after.